The present invention relates to a process for recovering copper from slags discharged from a pyritic smelting furnace such as a flash smelting furnace in copper refining. More specifically, the invention relates to a process for recovering copper from slags of the copper smelting furnace, utilizing zinc removed tailings in which the zinc residue or crust has had the zinc content recovered therefrom, said zinc residue having been discharged as distillation furnace residue or leaching residue during the zinc refinery.
Since there is usually about 1 percent of copper content in slags (hereinafter referred to as smelting furnace slag) discharged from a smelting furnace such as a flash smelting furnace, blast furnace or reverberatory furnace, it is required to recover the copper in some way or other to improve the yield of copper in a copper refining furnace. To this end several methods have heretofore been employed to recover the copper by providing a slag treating furnace (hereinafter referred to as slag cleaning furnace) such as an electric furnace or the like following the smelting furnace. According to one of the methods, the copper containing matte particles mixed in the smelting furnace slag are allowed to settle down by maintaining said slag at an elevated temperature for a period of time. There is another more positive conventional method of enhancing the copper recovery in which the slag is maintained at a high temperature in the slag smelting furnace while blocks or powders of pyrite or copper containing pyrite are added to the slag so that the matte particles suspended in the smelting furnace slag and containing copper are caused to co-precipitate along with the pyrite as it settles.
However, the method relying on the gravity settling of fine matte particles is inadequate in the copper recovery. The method based on the addition of pyrite or the like is considerably more effective with respect to the recovery of copper, but it is still not entirely satisfactory and has the drawbacks as will be mentioned below. When the pyrite or copper containing pyrite to be added is in the form of powder, it is necessary to blow such powdered ore into the melt of smelting furnace slag to promote the smooth reaction, for which purpose special equipment is required. Furthermore, dusts will inevitably be involved. When ore in the form of grains is used, it may be charged into the slag by gravity, requiring no special equipment, but the reaction rate is slow. A further disadvantage of the method by the addition of pyrite or copper containing pyrite is that due to the technique of co-precipitating the copper containing matte particles along with the pyrite, the so separated and recovered matte is of a low grade with respect to the copper so that a greater burden is imposed on a converter in a subsequent treating process. Still another drawback to this method is that it requires a great amount of energy to maintain the slag smelting furnace at an elevated temperature. For example, when the heating method by the use of graphite electrodes is employed, electric power of 80 KWH per a ton of smelting furnace slag to be treated is required.
On the other hand, in the zinc refinery the zinc residue containing gold, silver and copper is discharged as zinc distillation furnace residue and leaching residue in the pyro- and hydrometallurgical refining process, respectively. Since these zinc residues have a high percent of copper content, they are subjected to either a hydrometallurgical treatment or a pyrometallurgical treatment to recover the zinc. Typical of the pyrometallurgical treatment is the Waelz process in which the zinc recovery is effected by fuming. In the case of the distillation residue, a method is employed in which the zinc residue is subjected to magnetic separation and the non-magnetics containing a high percent of zinc content are repeatedly treated in a zinc refining process. The residue subjected to such treatment is discharged as Waelz process tailings or magnetically separated tailings. The tailings, which are herein termed "zinc removed tailings", remaining after zinc has been recovered from the zinc residue in a zinc refining process as described above contain values such as gold, silver, copper and the like, metallic iron and silicon. An example of the composition is shown below in Table I.
Table I ______________________________________ ingredients Au Ag Cu Fe Zn Si C contents 2.7g/T 600g/T 4.8% 58% 2.5% 8% 3% ______________________________________
Heretofore, such zinc removed tailings have been treated in a copper refining furnace, mostly in a smelting furnace or converter for recovery of the valuable metals therefrom. However, when the treatment is carried out in a smelting furnace, the reduction atmosphere prevailing in the furnace prevents the iron from adequately falling into slags, necessitating the limitation of the amount of the tailings to be treated. In the case where the treatment is effected in a converter, as the amount of the zinc recovered tailings to be treated is increased, there is correspondingly a decrease in the amount of the matte to be treated which is the original object of treatment by the converter. Consequently, from a stand-point of productivity, there is a limit in treating the zinc removed tailings by a converter. Thus, it cannot be said that any of the conventional treatment methods is effective.
In an attempt to overcome the foregoing drawbacks to the prior art methods of recovering copper from smelting furnace slags, the present inventor has discovered that in refining the smelting furnace slags in a slag cleaning furnace, the introduction of a charge of zinc removed tailings into the slags provide salient effects in copper recovery and economy of electric energy as well as making it possible to recover very effectively the valuable metals contained in the zinc removed tailings.
Based on this discovery, the present invention provides a process of recovering the copper contained in smelting furnace slags and concurrently recovering valuable metals such as gold, silver, copper and others in zinc removed tailings.